Strange vibration/noise

[its turbo time]

I recently put a torque strap on my car and i got her good and tight, but the only problem is now there is a strange vibration that occurs when the car is slightly accelerated and kept at low rpm's, its more obvious when the car is cold and it doesn't seem as bad when the heater is on. to me the sound is similar to the noise my car makes when the vents finally kick on. cuz my car usually takes a second for the vents to start breathing air, and when they do there is a light thud. and thats what the vibrating sound almost resembles to me.