[lithium]

Maybe try moving the ground. Is this running off factory power or aftermarket amp/hu?

 

[lithium]

Probably ground loop.

 

[lithium]

If it is white noise and the engine is off, then priably not a ground loop??

Ground loops can still occur with car off. It's just a difference in potential between devices. Im leaning towards another cause for this but its hard to say. Question is, does the noise exist with the factory tweeter but he can't hear it? If so than the root cause isn't the tweeter, its the factory HU/amp. At the same time, factory grounds can be pretty ****. Maybe running a new power and ground to the battery would help... Otherwise the OP needs a new source/amp.