I don’t know what blowing raspberries sound like other than a fart like sound . Never heard a speaker do that.
Can you send an audio clip?
Lacking that I would focus on the woofers, particularly the refoamed one.
With the amp turned off gently push the woofer EVENLY in near the intersection of the voicecoil and cone until the suspension bottoms. Listen for scraping sounds. Then?rapidly remove your hand. The cone should take at least a few seconds to return to its resting position.
if it returns rapidly you have a leak, probably because the woofer is not sealed to the enclosure. It is very important that this is sealed tightly. Know that since you have the grill removed air is likely to leak out of the holes the screws make for attachment. You can temporally tape over those holes to eliminate that leak. Leaks can be hard to localize. You can use a mechanics stethoscope ?or something similar to find the leaks by listening for a air rushing sound.
f you hear rubbing when you push the cone in you will probably have to repeat the refoaming exercise paying very careful attention to voice-coil centering.
Charlie Conger