So I just bought a 98 sl2 only problem is when AC is on at idle it makes a buzzing noise. AC off it doesnt do it. It is coming from the compressor when you raise the rpms to 1500 on up its quiet. You cant hear it in the car but can when your by the front of the car and you really hear it when its hood is up. Freon is good and other than the noise it works good. Does anyone have any idea. Thanks guys.

captain obvious says compressor is bad

Lol well any rhym to reason y it only makes noise when its at lower rpms

I 2nd the compressor may just have a bearing going bad,slowly.I'd start checking for cost for a new one from any of the auto stores to get a idea of real cost.

Its pretty expensive I may buy one at the junk yard is that a good idea. They are45 bucks there.

with used its very possible to get something in the same shape as the existing one

only other possible thing would be the belt tensioner , but im still with the compressor

The only thing i dont understand is why does the noise go away above 1500rpms? That doesn't make sense to me

noises can come and go with rpm , and the load on the parts

It could be low oil. If there isn't enough oil mixed with the freon it will make noises at low rpms. When you bring idle up its forcing more through faster. Quieting it down. Could also very well be the start of the clutch bearing going out.

Even if you get a compressor from the junkyard, most junkyards give you a short warranty. So if you get one from the junkyard I would just get it on a day that you install it the day of or shortly after to see if you have to return it.

Well noise hasn't changed or got worse and still blows cold. It's not a metallic metal noise at all. It sounds like a cicada the bugs lol. It's strange. My mechanic friend said he would let it go until it got worse he doesn't think it's a bearing though.