Headphone,

 Discribe the noise....that would help.  How do you have them wired, thats number one. try using one amp. When problems occur, alway go back the the simplest form. I.E. one speaker one amp, then work your way back to where you want to be, you'll find what you've done wrong and what the cause of the problem is.

EP

Wired correctly? are you saying that Mono both channels is correct? did you check them for phase. If they are wired out of phase and you push them to hard trying to make bass come out of the cabinet, you could be flexing the cones to the point that they buckle and will make a God awful racket.

 If both drivers are facing the same way you'd wire them the same way  I.E. Positive to Positive on both drivers, if the are mounted opposite of each other then they should be wired opposite of each other i.E. one driver wired with the positive going the the positive terminal and the negative wire going to the negative...and the other driver would be wired positive wire to the negative terminal on the driver and the negative wire connected to the positive terminal on the driver.

 The reason I mentioned go back to a single amp was just in case the happen to be out of phase with each other, this would probably make more of a difference if the were stereo amps bridged mono.

 Another scenario would be... if the drivers are clamshelled  together, both surround could be touching, which will offset the VC in its gap, in that case you might need to build a spacer to separate the drivers surrounds from touching each other.


  Headphone,,,do you have any bass coming from the cabinet, or is it just the racket, and no bass??

EP

Headphone,

 It sounds like that drivers gone bad, but I'd take it out and verify before you just pull it out and through it away.

BZ

I had a sub, at one point, which had one of the voice coil leads split. At rest the circuit would be complete and the speaker would start to push forward, only to open the circuit. Then when it would start to come back to resting position, it would close the circuit again.

Talk about an awful racket of arcs! A little solder fixed it right up and it worked great. That's one of my old school pioneers that's been retired(worked when retired) and is wrapped up in my garage.

Headphone,

  Using PVC would work just as well, if you had the correct size,  did you check the plans and check the size of the coffee can????
Also if you can't find PVC the correct size, the port doesn't have to be round, find the same area in a sq. and build it to the correct length out of MDF, round over all the edges as large as you can and the port noise should go away!!!!


BobZ