Strange sounding AC @NCL
 

Sitting in Tynemouth at about 1250PM Friday. aircraft make their approach up the coast before turning into NCL runway.

I heard what sounded like a helicopter in the distance getting closer - quite a distinctive "clatter" Dismissed it as the police chopper or whatever but when it got closer the sound got deeper and evolved into a turbo prop.

Couldn't see it from where I was. Obviously we get a lot of turbo prop twin engined stuff over hear, but I've never heard anything like that.

What was it?

Thanks,

Tyne

Taking a guess, it could have been a Chinnock.
Seen and heard a few in this neck of the woods.
Your description seems close enough.
They have a distinctive clatter which would rattle windows
Flying away from the observer they can sound like turbo-props.

There has been
 

an MH-53 out of Mildenhall up there in the past few days. May be what you heard,