Muted D string
 

I've a p-bass with a D string that doesn't seem to have the attack / twang as the other 3. The problem is worst when fretting around the 5th - where the string feels kind of "rubbery". It's fitted with a fresh set of Fender 7250m's

I'm used to dead spots on the G string around 5-7th frets, so it might be that - but I've tried a fat finger and whilst that helps a bit, it doesn't really (re)move the problem. I've also played around with the pick up height.

I've read on here that this can also sometimes be a result of a bridge problem. If that's the case, what should I look for? (It's currently fitted with a BadAss II).

If it is a dead spot, has any one seen them go away when moving the neck onto another body?

Are there any other things I can look for (I've done the usual action / truss rod tweaks).

Cheers

It's fitted with a fresh set of Fender 7250m's
 

Did this occur after the string change, or was it the same with the previous set?

No - same as before. A bad string was one of the things I was trying to eliminate.

I had a bass once that I thought had a dead spot. I pulled the neck off and found that the threaded inserts weren't flush with the neck. I ground them down with a Dremel and it fixed the problem.

It may be that you're "twisting" the string when you're installing them. This can make a new string sound dead or lifeless.