I have a 2013 mcs with 94000mi. So its getting pretty cold out now and latly ive been noticing a tapping noise from the driver side of the engine. From looking around n listining it sounds like the vacuum pump. I noticed the same noise earlier in the fall but it usually went away when warmed up. But now it seems to be a constant noise. And sometimes it feels like wen im at a light the brake pedal kinda goes down a lil with constant pressure. Aleo on my scan gauge i notice some mornings it reads lik negitive 13 for boost/vac idk if its accurate or realated figure id throw it in. Is there n easy way to test the pump? Is the constant tapping sign of the pump starting to go? Any help would be great!