Hafler DH 500

Thank you for your informative reply. I don’t see the switch blinking when the amp goes off for 2-3 seconds and goes on again intermittently. The switch is new, I replaced it a couple of months ago when I got it from a local seller. I also cleaned the heat sink and it is not gunky dirty. I CAN HEAR “CLICKING SOUND” when it goes off. 

Does that occur with all sources, or just one? How frequent are these malfunctions? Can you hear the relay clicking, with no input to the amp(ie: preamp turned off or disconnected)?

I shall have to test if the amp does this (clicking sound without input source), and also test with other source. I will keep in touch until I come back from vacation. Thank you very much! You are very helpful.

P.S. The frequency is every 2-3 songs. It goes off 2-3 seconds and goes on again.

Those tests should reveal a lot.  I'll be watching, for your further info.   Hopefully, we'll figure it out!   Have fun on your vacation.