Help with whistling ac noise and clacking noice too

Volvo S 70 GLT SE- 2000

I just had a new compressor put in for my airconditioning and it works fine. Only now I have a whistling or a noise that sounds like guitar feed back when I shut off my car and sometimes when I start it. I also have a clicking or taping noise that has been going on for over a year inside my dash or ventilation system. It drives me nuts. I was told the whistling feedback noise is due to a fan going bad. I didn’t have this noice before they replaced the compressor. What is the cause and how can I get rid of this tapping clicking noise that has been going nuts for so long?