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[mcd840]

I will try and break this down as best I can -

The other day when I started the car I noticed a "humming" sound which I can only seem to make out whilst inside the car. I gave the car a rev and the humming increases with engine speed, it can also be heard when driving the car. Also noticed that my a/c pump is a hell of alot louder than usual and there is also the sound of "swooshing gas" which echos from the vents, to be fair I did always get a slight noise as the pump engages but then settled out but now constantly noisy, if I give the car a rev the pump gets even noisier, just to add the a/c was re-gassed a few weeks ago and is fine and cold.

In regards to the humming sound the signums m32 gearbox bearings do whine a little which is a work in progress and I dont think this noise is related.

Lastly the car had the timing and balance chain kits replaced a few weeks back (gm kits) and has since been back at the garage because of a rattle from the chain area when started from cold, goes away when warm, garage removed rocker cover and looked at timing chain, all tight and there happy with it, im not convinced, even more noise now than before they were replaced. looking for opinions please

Cheers

[tidla]

Take the aux belt off to eliminate any noises from air con/alternator/ idler pulleys.

The crank case valve on the top of the engine  are a GM stock item and can make strange noises come from the engine.

Loosening the oil cap while running ( keeping the cap in situ) to see if any noises change.

All cheap to try.

[mcd840]

I was actually starting to think its down to the belt tensioner, I drove over a hundred miles last night and debatable if I heard it as I had the a/c off, also when the a/c is on and I give the car a rev the noise gets worse which I think is from the a/c pump, hopefully its just a tensioner issue

[mcd840]

Quick update, whilst driving earlier I heard the a/c pump re-engage itself a couple of times (can only assume it cut out). Got home, looked in the pump area, switched a/c on and a squeeling sound from the pump, smoke from the clutch/pulley, switched car off, 15 mins later re-started. a/c started normally and still seems to be working