Okay, installed new compressor and drier the other day. Now at idle in Park it makes a very faint noise. When at idle in gear it makes a racket. When the A/C is off it makes no noise. With A/C on going down the highway it makes faint noise. Should I have hooked everything up and then evacuated the system before adding R134a?

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'85 300SD (formerly california emissions)
'08 Chevy Tahoe
'93 Ducati 900 SS
'79 Kawasaki KZ 650
'86 Kawasaki KX 250
'88 Kawasaki KDX200
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'72 Triumph T100R