Even after replacement, iPhone 6 loudspeaker stops working

So, my iPhone 6 took a swim in the Gulf of Mexico last month.. I had thought the phone was completely dead, but-- miraculously-- after doing a self-repair which initially entailed taking the phone apart, disconnecting the battery, cleaning the internal parts with 99% isopropyl alcohol and then replacing the battery, replacing the charging dock element and finally, replacing the display, I was able to get my iPhone back to normal (almost).

After turning the phone back on, everything worked like it had before EXCEPT the loudspeaker. It vibrated just like it had before, but audio -- when played-- sounded distant and tinny at the very best, and you had to hold your ear up to the loudspeaker to even hear that much.

So, I ordered a replacement speaker kit, opened the phone up again, took out the old one and put in the new one. Closed it up, turned it on and VOILA! The audio came blasting out like new! I was nearly very pleased until I checked the vibration function and got nothing from this new element. To make matters worse, that clear audio coming from the speaker now suddenly crackled off too, and the phone sounded no better than it had with the previous speaker it had inside.

I assumed that the replacement speaker must have been faulty, so I ordered a new one from a different company. When that arrived, I took the phone apart again, replaced the replacement speaker with a re-replacement, closed it up, turned it on and....

....clear audio for about... 30 seconds....and then *CRACKLE CRACKLE*. Back to tinny, faint audio and a very very feint vibration.

What could be causing this? Is there a short happening somewhere in the phone? Is there a bad connection that I should be looking into?

What kind of solutions do I have? I have thought of getting an external case that has speakers built into it, if nothing else, but this still won't give me my vibration function back and it's not an ideal solution.

Any suggestions would be greatly appreciated.

Thanks!