Air conditioning, replaced the pump twice, donèt want to replace again

One year ago started to make a noise. Replaced the pump, after six months it quit, had a leak at the h valve replaced, three months later with another noise had the pump replaced again, almost immediately had a worse noise(like a fog horn and never consistent. Finnaly blew the pump up. Mechanic replaced the pump again for the last time on warenty, he thinks there is something floating arround in the rest of the system causing the high pressures. Any ideas I will try to replace the cooler or and the evaporator, Any suggestions on which one to try first etc.