1999 Honda Civic Occasional Strong Whistling Sound when ai

Air Conditioning problem
1999 Honda Civic 160000 miles

I brought my 1999 Honda Civic Lxi (Manual) to an air conditioning shop and had my condenser, evaporator, expansion valve and air filter replaced. After the repair / replacement of the said parts, the air conditioning went back to normal but after a week I noticed that there's an occasional strong whistling sound (not the same sound if freon is leaking) on the side of evaporator. The sound only comes out if the car is moving, but not if it's on idle. I brought it back to the air conditioning shop and did a test drive for them to hear the strong whistling sound, unfortunately they don't know it's cause and on how to fix it.

Any idea what's the cause of my car's problem and how to fix it? Thanks :-)