From Dave Sergeant G3YMC

I can answer Peter G8AFN's questionaire right now with no need to switch my
receiver on on Saturday morning.  DCB39 will be S9+18dB +/- a dB or so, as
it always is apart from very occasional short lived QSB usually mid
evening.  Natural band noise will be around S3 at that time of day, but is
S7 in the post dawn period.  What my local QRN level will be is unknown as
I may have S9 low energy fluorescents, or my local TV carrier generator may
be on at S9 on 137.2.

There is little to be gained from S meter reports because of the variation
of sensitivity and linearity of these, even relative to background noise
level.  The real acid test as to whether you have enough sensitivity is as
to how well you receive the natural background noise.  You should be able
to hear static crashes and natural thermal noise comfortably above your
receiver noise, and if you have a tuned front end this should peak very
nicely. If you have a totally quiet band background noise which seems to be
mainly your internal receiver noise you have by no means enough
sensitivity.  At this QTH during the daytime the base background is around
S3 with frequent and constant static bursts to S6 or S7. Loran is also
there, but it seems somewhat variable and unpredictable at this QTH, being
nothing like some report.

A quick test to see whether intermods are your problem (in central England)