Loud hiss coming from bass head

[coffee_king]

Hi Guys
Before I take this to my usual repair guy I thought I'd drop a quick post on here to see if anyone has any thoughts on a home repair?
My Ashdown ABM500H seems to me creating quiet a lot of hiss. (Its not due to having the treble up high)
Its also coming out of the DI (Its very annoying in my IEM) so it wont be the cab.

Now of course its not noticable once the band all kick in, but it is very hissy.
Any thoughts on whats up with it?

I'm using it with an Ampeg SVT 410HE by the way.

Cheers dudes.

[rogerstodge]

This may help you matey.
http://basschat.co.uk/topic/51381-noisy-hissing-ashdown-abm-500-rc-evo-iii-head-is-this-normal/page__fromsearch__1

[MoonBassAlpha]

Is there a snake trapped inside?

[RAY AGAINST THE MACHINE]

Have a bump. , as I can't offer any advice here , other than not to play any white snake .

[coffee_king]

So, I took this into Steve at Musical Electronic Repairs & Spares (Within Madhouse Rehearsals in Birmingham) and he's sorted it.
All it was apparently was the valve was seriously on its way out (I guess I should have checked this out myself first).
So now theres no hiss at all (apparently)
But anyway its fixed now and I'm picking it up later, so will review it shortly.

Thanks for yoru advise everyone.