I don't know anything about Manch (I was born there and vowed never to return!!). However.. at West Drayton (and most other large units) controllers have the facility to link two or more frequencies during quiet periods. It's called "bandboxing". In my experience this can cause transmissions to sound slightly muffled. Another likely possibility is that he was using a handset rather than a headset. When traffic is quiet some ATCOs take their headsets off and use a thing that looks like a telephone handset. If ONLY they knew how utterly dreadful they sounded they probably wouldn't do it.
Be honest - tell the guy is is difficult to read.. If it's not down to obvious problems he should report it and get it checked out.