Paul P

Last night on the way home from work, I thought I heard whistling coming from the engine bay while driving in 4th gear at around 50-60mph. Now it was a bit windy so I thought it might just be the wind, after about a mile or two, the noise went away.
When I came to my favourite roundabout, I blasted the car round the corners and put my foot right down to see if the car has lost any response. No, the car was just as good as usual, great acceleration etc.
When I got home, I had a browse through the SIDC FAQ booklet and came across an article on the whistling noises due to the dump valve not closing properly. My car is a MY99 UK model. I am still unsure whether my car had suffered from this while on the way back home.
If anyone can answer the following questions, then that would help:

(1) Does it sound as if this was the problem?

(2) Will the problem return or was it that the dump valve did not close properly the first time but sorted itself out after that?

(3) Will the problem return? The car seemed fine for the remainder my journey (over 20 miles).

(4) What effect does this problem have on the engine?

(5) If it is the dump valve and the problem persists, how do you fix it?

Many thanks in advance,

Paul.