strange intake sound

[gndeligirl]

help, I am a new owner of an 87 gn and just recently got the car back on the road. After spinning arod bearing the car has sat for a year. I had a used engine installed. minor upgrades chip, regulator, injectors, exuast, open element intake. Car runs well but I hear a loud fluttering sound comming from the left front of the car. Always happens after boost while lifting off the throttle. I cant remember if this is normal. any info would be appreciated.