SIR - I write in response to the letter from J Horlock, Just what is that humming in sky?' I think I may be able to enlighten you. It is a plane - either a C130 Hercules or a Britten Norman Islander - flying in a very tight circle over Worcester at about 10,000ft.

These two planes have been driving me insane for weeks!

With the aid of binoculars and the internet, I was able to identify them as military.

After contacting the MOD low flying department, it would appear they are testing new equipment and must fly in this pattern. They will not confirm or deny whether the testing will eventually end.

I am at the end of my tether; the incessant droning of the plane engines is so irritating. I work outside so I can never avoid this constant drone.

Might I suggest, next time you hear this noise and the sky is clear, you look up and will be able to spot the plane; the Hercules has four engines and the Islander has two engines and is red.

The phone number for MOD Air complaints is 020 7218 6020. Perhaps, if enough of us complain, they will have to stop doing the testing over Worcester.

M BROWN, Worcester.