Noise in an old NAD 3020

I bought an old NAD 3020. It works great except, when I first turn it on I get distortion for about two minutes. After that I only hear the distortion when I turn a knob. Anyone know whats wrong here?
The potentiometers are probably dirty and need to be sprayed and worked with some tuner spray. That is a common problem with those units.

As for the turn-on distortion, I used to have one that did that. It seemed to be exacerbated if I had the "loudness" switched in for some reason. But the amp sounds much better after it has been powered up for a while, so my suggestion would be just to leave it powered up all the time. It doesn't draw much power at idle, and that way it will always sound its best.
Check for bad caps in the power supply?
I just picked up a used NAD 3020B which seems to work fine. Unusual is that every time I powered it on, it seems to send a kinda of vrooom.... sound to my speakers for a second. I've sprayed the inside but still the same. Is this common with some units and what is the best DIY repair?

My recently sold NAD 3020 use to "thump" when turned on and right after that one channel sounded like big sunami waves. Those noises usually disappeared in a couple of minutes.

The solutions were: Push mute button before powering on and let pass two or three minutes to get things warmed-up.

After that it should sound nice.

Good luck