05 Yukon XL 4x4 Rattling in bellhousing area with AC on

[HighestStorm]

Hello new to the forums, just bought my 05 Yukon in december. Bought it at $214,000 mi it's around 216,000-217,000 now. From the Carfax history when I bought it and from the owner of the dealership who sold it to me personally because it was his personal vehicle, he showed me and the Carfax showed me that all the major mechanical maintenance had been very well kept up, and he did a lot of work to it to sell it like new shocks, transmission flush, a new tires, Fresh oil, so all the major mechanical things were really well taken care of but my AC is starting to give me issues. At least I think it's my AC. Whenever I start the vehicle if my AC is running when I start it a loud rattling starts, everything still works fine and whenever the vehicle is moving the sound goes away or I can't hear it. Upon investigating and doing research I thought it might be one of the ac pulley bearings or ac belt tensioner bearings but whenever I go underneath and listen to the rattle sound it's not coming from the compressor or belt area, it sounds like it's coming from the bell housing or exhaust area. Saw one video on YouTube that somebody had the same issue and getting the catalytic converter replaced fixed it and saw another video that said that it could be the AC clutch bearing or tensioner bearing but it doesn't sound like it's coming from the belt area it is more towards the bell housing. Anybody have this kind of issue and can help me? It would be greatly appreciated. If it has to do with the AC or the catalytic converter I know that that can both cost upwards of $500 each job but I don't want to fix one thing if it's a different thing and then have to do both and spend twice the money.

 

[ks03]

I’m going to throw out another possibility for you. Coming from the bellhousing area, my first though is a cracked flex plate. Typically they’ll start out only making noise in park or neutral at idle. Sometimes they sound like a rattle, other times it sounds more like a rod knock.

 

[HighestStorm]

I thought it was rod knock at first so I might look into that I'm just trying to fix the right thing and I'll fix something that I don't have to. Thank you I'll start looking into that as well.

 

[HighestStorm]

I’m going to throw out another possibility for you. Coming from the bellhousing area, my first though is a cracked flex plate. Typically they’ll start out only making noise in park or neutral at idle. Sometimes they sound like a rattle, other times it sounds more like a rod knock.

How hard of a job is it to replace the flex plate?

 

[OR VietVet]

Welcome to the forum from Oregon.

@ks03 beat me to it. Does sound like the flex plate. There is a cover on the bottom front of trans that should be able to be removed and look in side there to see if there are obvious cracks. If cover is removed the noise may sound louder and then you can find problem easier. If yo get in there with a flashlight and look hard enough, if there are cracks they will look like little spider web tentacles from the center area on out. It could also be loose attaching bolts. Would need to at least unbolt the trans and move back or drop out for flex plate access.

By the way, when you crank the engine when starting, the a/c clutch has no power to it till the engine does start. If you turn the key to KOEO and a/c is switched on, you may hear the clutch engage but when cranking, it will free wheel and no actual a/c function is happening and then when release key, when engine is started, the a/c will continue to work like normal. That is done so the starter does not have to spin the a/c compressor during the engine crank to start.

If you have a mechanic's stethoscope it will help immensely with noise searches.

 

[treehan77]

Take the a/c belt off and start it, then you will know for sure if it is NOT that

 

[menusk]

It’s your ac tensioner. Usually Theo means your ac compressor is going out too.

 

[BCull68]

Hello new to the forums, just bought my 05 Yukon in december. Bought it at $214,000 mi it's around 216,000-217,000 now. From the Carfax history when I bought it and from the owner of the dealership who sold it to me personally because it was his personal vehicle, he showed me and the Carfax showed me that all the major mechanical maintenance had been very well kept up, and he did a lot of work to it to sell it like new shocks, transmission flush, a new tires, Fresh oil, so all the major mechanical things were really well taken care of but my AC is starting to give me issues. At least I think it's my AC. Whenever I start the vehicle if my AC is running when I start it a loud rattling starts, everything still works fine and whenever the vehicle is moving the sound goes away or I can't hear it. Upon investigating and doing research I thought it might be one of the ac pulley bearings or ac belt tensioner bearings but whenever I go underneath and listen to the rattle sound it's not coming from the compressor or belt area, it sounds like it's coming from the bell housing or exhaust area. Saw one video on YouTube that somebody had the same issue and getting the catalytic converter replaced fixed it and saw another video that said that it could be the AC clutch bearing or tensioner bearing but it doesn't sound like it's coming from the belt area it is more towards the bell housing. Anybody have this kind of issue and can help me? It would be greatly appreciated. If it has to do with the AC or the catalytic converter I know that that can both cost upwards of $500 each job but I don't want to fix one thing if it's a different thing and then have to do both and spend twice the money.

I have the EXACT same symptom....noise is very random, usually only occurs when first start/drive, then goes away quickly although I sometimes immediately turn AC off... the other day it did it and then I notices AC not blowing cold, took a look no AC belt! So I just ordered and received and tensioner/belt kit for Gates.. It has a TSB sheet with it.. explains the "Slugging" issues with GM AC Compressors... hoping my tensioner/belt kit is THE problem!!

 

[OR VietVet]

Welcome to the forum and good luck with the hopefully repair job.

 

[HighestStorm]

Just got everything repaired. The rattling noise was the flex plate, and the starter solenoid was going out due to the flexplate being cracked. And the sluggishness when giving gas turned out to be the rear knock knock sensor being corroded with water. The knock sensor being corroded fouled out cylinder 7 spark plugs so I got new spark plugs as well. $600 in labor for a shop to replace the flexplate/flywheel and starter as I didn't have the tools necessary to drop a transmission out to change that, not including the cost for the parts for it, I bought them myself. Parts included new battery, new starter, new knock sensors and harness, new intake gasket, total for parts was around $700. So $1,300 later it seems to be running fine now. And just in time for my birthday tomorrow. Good birthday gift for myself. Thanks for the tips on the flex plate.