I can't help you out with your kompressor noises.
But I can help you figure out your trans kicking down.
If you're going fast, say, 60 mph and you floor into kickdown, then your car should kick into second gear, if you are going between 60 and 90 (roughly) and you punch it into kickdown, it will kick into 3rd gear.
WHen you floor it to just the floor (not through resistance point), the car will shift to one gear above the lowest possible gear for the speed you are going. IE, the car knows you want to get going, but not to max power.
If you floor it into kickdown, the transmission will pick the lowest possible gear for the speed you are going.
Going 30 and below, floor into kickdown, kicks into 1st gear.
Going 60 and below, floor into kickdown, kicks into 2nd gear.
Going 90 and below, floor into kickdown, kicks into 3rd gear.
Going 120 (better not be!), floor into kickdown, kicks into 4th gear.
Keep in mind these are all rough estimates for your transmission (5 spd auto, 722.6 I believe). I hope this all was somewhat clear for you.
2006 E350 w/ 155k miles (Daily Driver)
1993 300E 3.2L Sedan w/ close to about 300k miles
2003 E500 Brilliant Silver (Had 217k miles when totalled!)
1989 300E with 289,000 miles (had for <1 yr while in HI)
03 CLK 500 cabrio (Mom's)
2006 C230k (Dad's)
1999 S420 (Mom's/Dad's)
2000 C230k Sport sedans
2001 CLK320 Cabrio (Mom's)
1995 C280 My First Mercedes-Benz... (155k miles. EXCEPTIONAL AUTOMOBILE. Was Very hard to let go of!)