When i start up my computer there is a loud noise from the fan (i think)it gets so bad you think it would take off,also every so often i get a clanging sound its a dell computer under warrenty but dell have not been very helpful,and if i phone them its not a cheap rate call.
Fans aren't usually that difficult to replace. I take it you mean one fixed to the case, rather than to a chip heatsink ? If under warranty though, do think before invalidation.
I'm unsure about clanking sounds. That from the fan also, or from Windows finding an error ?
Ideally get on Dell's case and insist. If you get fed up check if you can get an identical fan from the Net (or Maplins if you have one near you) and take the plunge.
Unscrew/open case. Check where wire from fan goes and which way around so you can put the new one back identically. Disconnect fan wire from board. Unscrew old fan from case. Screw replacement fan to case. Reconnect new wire where and way around old wire went on the board. Close & screw up case.
Check to see that nothing is catching on the fan.
Mine did the same a while ago and when I removed the cover, I found a wire had somehow come unclipped and was dangling in front of the fan. causing it to rattle like mad ... sometimes quite loudly.
I'm fairly sure my cover is only held on with 2 screws (though it may be 4). Unscrew the screws, then the cover slides off - you should then be able to see the fan, etc, without removing anything else :)
I'm told you should never put a vacuum cleaner inside a computer due to possible damage from static electricity however I can't see anything wrong if it has a cardboard tube extension sellotaped onto it.