Magnet valve??

Hi everyone.Im new to this forum and this is my first post.Unfortunately my first post is regarding a problem I am having.
I have a 99 s4 avant(I live in Sweden) and it is losing power every now and then.It seems to go great when it is cold but when it heats up in the engine bay I start to lose power.I have checked my vacuum hoses and seen that one was not very tight so I fixed it.Otherwise I cant see anything else that looks wrong. My question is , there is a, in Swedish it is called magnetventil,which directly translated means magnet-valve.This is powered by a 12volt signal and it seems to be making a strange noise.It seems as if it is being switched on and off in quick succession and sounds a bit like a broken relay-switch.Should this be doing so or should there be a greater pause between when it should go and not?
Please,if there is anyone who has a clue what I´m talking about, can you shed some light on my situation.

Chrism.

can you take a picture of this and post it on here.. there are many electronic valves that make fast clicking noises in the engine bay.

I would check your Thorttle Body Boot as well. These are known to be torn once in a while..

I checked with Audi today and the valve in question is a part of the active-karbon-fiber-filter system.I went out for a drive this evening and it went really well.Then I checked if the valve was making any noise and it did.So I can almost rule out that.
I have already checked my TBB and it was whole.Doesnt seem to be a big problem here.My Audi dealership has never sold one when I asked if it could be that.Ive been checking the vacuum hoses as well and none were torn but Ive ordered a couple of small ones just for peace of mind.
This problem only seems to happen when the car gets warm,never cold.And not all the time either.Does anyone have any other ideas,before I have to leave it in for a full diagnostic.

Thanks for your speedy replies from my first post.