Curious Sound problem

Dear fellow Simmers,
for some unexplained reason I have just lost the tyres/asphalt sound on my runways.Curiously,the sound returns once I turn onto a taxiway.I have'nt fiddled with my settings and the only thing I've added in the last 24 Hours is Manuel's S.P.3+Airport Chart v 5.0 and the wonderful FS Water from Flight One Software.
It's no fun landing without the reassuring sound of contact with terra firma so any help will be gratefully received.

kevin