Hitachi
AC Making noise

I bought Hitachi Window AC around a couple of years ago.

On turning it ON, it is making noise. Looks like the noise is coming from Compressor, it goes high and then low and sometimes goes off. And sometimes it starts in the middle. But it is always... when Compressor is running.

Running on vGuard VGSM 400 stabilizer but noise is coming even if Run directly without Stabilizer.

This noise generally comes when there is peak time (High demand of AC).

Is this due to low voltage?

Is there a problem with stabilizer itself?

Is there a problem with AC compressor or some other part??

Kindly answer as this is out of warranty now!.. :(