Possibly an AN -12?
I dont know if they still operate , but they used to use East Midlands Airport a lot.
Coincidently a few nights back , 1am two nights running there was an overflight here at Wisbech.
Certainly not much like a Herc.
In the distance engines sounded a bit out of sync, then settled down to a long drawn out drone fading to out of sync again.
Other than that how about a P3 Orion, to Mildenhall perhaps?