I have 1998 Nissan Sentra and when I turn on my AC a loud noise comes on?

You have what are called reed valves in your compressor.Tiny metal flaps that make it work.Over time the reeds break off and causes the noise and makes it harder for the engine load to turn the compressor,thus the little shake.Make sure when they replace the compressor,they also do the expansion valve and drier which are sure to be contaminated with metal particles(reed valve material).

It could be several things. the fan that blows the ari could be going bad. If the same noise happens when the vent is on and the AC is off, then the problem is the fan.

It could also be a compressor going bad.

this is a chrome steel conceal on the backside of your converter. it is completely nice to eliminate it. in the early days of converters whilst police automobiles concealed they have been inflicting grass fires. that's the only reason for them in the 1st place once you get the motor vehicle up in the air take one area of the immaculate and bend it so some distance as you could. shop repeating this after repeated bending the immaculate artwork hardens and makes a sparkling injury. Sawing does no longer artwork. An acetylene torch will do it in some seconds. sturdy success.

I would say the problem is with your A/C unit and if you take it to a certified A/C service shop they can be a little more exact in their diagnosis.

sounds like you have a bad bearing on the compressor clutch.