Loud Synchronized bang at about 4-5 sec intervals coming from alpha 1. ?

[Eastboundndown]

So, I replaced the shift cable from merc. 5.7 to outdrive and still same problem, then I swapped lower unit out (with a used one), then I swapped the shift lever out because it seemed a little “sloppy” but nothing. Another merc/alpha boater said it could be a bent or worn shift shaft. Has anyone ever ran into this? Could a bad gimbal bearing cause this? Not sure what to check next?

 

[alldodge]

Sure its the drive and not the motor back firing, as in does it do it with the drive off?