Black Heart Little Giant rattling

This can be one of a few potential problems.  I am not familiar with Black Heart's, but I know about combo rattle.  It could be the chassis vibrating against something or it may be a tube.  I would carefully try to isolate the source.

I would not start touching the circuitry of the amp with out discharging the filter caps, especially if you have little experience.  Besides the health risks, you can also void the warranty.

I also wouldn't rule out mechanical noise from the power tube.  This can sound like metal on metal and be very, very annoying.  If you are getting noise when you tap on the amp while it is off, this may very likely be the source.

It would be hard to tell you how to go about solving this problem without being more familiar with amp.  I would, however, look for spots in the construction that would be susceptible to vibrations.

If it's new, it comes with JJ tubes, unlike the first few batches that came with chinese tubes.

The rattling could very well be the EL84 cover that wasn't screwed in all the way.  Whatever you're doing don't touch anything INSIDE the amp or it really might kill you. But anything on the chassis is safe. Unplug the amp from its power source, flip the on/off switch a few dozen times and  then take the chassis apart to verify the screws. As long as you don't reach inside the amp for any reason ( like flipping the amp upside down ), you're safe...

It also could be something in the room vibrating because of the soundwaves reflections.

Glad you were able to locate the source.

The Class 5 also has had rattling problems, but they seem to have been sorted out and the later serial numbers are sans rattle. 

The Marshall Vintage Modern Forum (which I am a member of) has a great section for the Class 5 because the designer did both the VM and the C5.  He is on the forum and answers many questions!

Here is the link:  http://marshallvintagemodern.com/viewforum.php?f=31 if you are interested.

I should be picking up my Class 5 today!!! 

Good luck with remedying the problem.

When the Amp is off (and cooled off!), it is fine for you to pull the Tube out.
    Just remove it, and then put it back in. Make sure you notice where 1 Of the Pins on the bottom of the Tube is "Missing", as this is a Key. The Tube Socket will have a spot with no Hole to match up with the "Missing" Pin.
    Put the Tube in Straight, and make sure it's seated fully and evenly into the Socket.

    Now, after re-seating the Tube, is it feeling more solid? If it still moves too much, then maybe the Tube Socket needs to be tightened. This should be a no charge deal from the Dealer's Tech. After all, it's a brand new Amp, and it should be "Tuned Up" and in proper working order, when it leaves the show room.
    Tightening a Tube Socket is about as in depth as tightening a screw. So, there should be no trouble from the Dealer on this. None. And there would be no need to "send it off to the Factory", or any other B.S. It is a very simple operstion.

    If the Tube DOES seat well, your problem should be rectified. If not, maybe try a new Tube in that slot.

    Good luck!

Old thread now but I thought I'd let you guys know whats happened, incase anyone else has this same problem with the blackheart LG.
I took it to the store, could barely hear the rattle there cause the lighting fixtures were rattling crazily when the volume was up at 10. The guy did say he could send it away but I thought it'd be a waste of time so took it home.
I opened it up, took out the preamp valve and tapped again, no noise, tapped the valve, bingo, the valve is s*** so a JJ ECC83 is on route to my door.

Just to make sure, a 5watt amp with a single EL84 won't need rebiasing if I chose to change the power amp will it?

Cheers Chris, I'll be doing that soon.