1997 Oldsmobile Achieva car makes clicking sounds.

1997 Oldsmobile Achieva car makes ticking or clicking sounds. When cranked, it cranks ok, but it immediately starts making a ticking sounds. Maybe 3 or 5 clicks a second I would guess. So fairly rapidly. Mechanic says the serpentine belt is tight and does not think it needs replacing. Water pump was replaced but it still makes noise before and after the replace. When the car drives, it seems to go away (or the engine noise is covering it up, but I really think it goes away mostly), but when idle, whether its in park or drive it starts again. It's quite loud. After you've driven and you stop at a red light or something and are idling you can hear it. So the car is in drive at this point, with the brakes applied. With the brakes applied you can also feel this ticking slightly in the brake pedal. The brakes seem to work fine and are very responsive.

The mechanic doesn't think it's anything in the engine itself, and that there is something hitting the belt maybe causing it?

Another sympton is the ac compressor is broken so there is no cold air, I'm not sure if related or not just mentioning. The car drives fine, it accelerates fine, does not sputter or anything, and transmission (automatic) shifts fine.

i have the 1997 Oldsmobile Achieva SL Series II 2.4L L4 DOHC 16V
thank you