Buzzing noise in cabin help please

[Caspon]

Hi everyone I was hoping someone could help me with my problem. For context I have a 2007 3.0si roadster which I recently bought. Ever since I've noticed a buzzing noise at higher speeds around 40mph and above. It's only audible really with the roof up and is drowned out with windows down. It sounds like its originating from behind me to the right just around where the seatbelt comes from. I have my seat all the way back and if I try move it back further it is touching or is already touching the panel behind. I remember moving my seat forwards and still hearing it so I don't think its that. Would anyone have any idea on what it is and how to fix it.
Thanks
Casp

 

[Sidewaze Samm]

Have you had a passenger hear the noise?
If not, then certainly get someone to listen for confirmation of the area it's originating from: sometimes it's not coming from where the driver thinks it is.
Does the noise change if you apply tension to the seat belt?

 

[Argyll Andy]

Is it buzzing as in an electronic buzzing?

If so I had the same in a speaker behind the seat from a cheap Bluetooth adapter I was using to stream music. Didn't matter whether the radio was on or not. Disconnected it and it stopped immediately, only effected the one speaker for some reason.