someones already said it, but I'll say it again...
mmmmmm............ fried batteries..................aaaaarrrrhhhh!!!!
Firstly, I would consider not buying the 2400 NiMHs again ( I don't know if you have other packs of the 2400s besides the fried ones). Since they are not something which is common in RC, they may not be too tolerant of high charge/discharge rates, ie it might not be the charger. I have seen RC packs take alot more than their nominal capacity and survive.... it's not good for them but I suspect 300mah extra wouldn't usually make an RC cell explode (well at least not when re-peaking) Take note that 2400 may only be their NOMINAL capacity
They may have high voltage or be a lot cheaper than the matched packs, but there are other cells out there which are cheap and very similar to the racing cells. Ideally, stick to what most racers use if you can.
Secondly, it seems extremely odd that a $265 dollar charger does not have a peak detect function with auto cutoff, but does have a digital voltage readout. The fact that you said your charger has "peak detect autocut circuit with mosfet" written on it should mean that it will switch the charge off itself, eliminating the need for you to switch it off. I suspect that unless the circuitry is dodgy, this is actually what's happening when it beeps, but in the case of the 2400's it's just not beeping early enough to stop the cells from overcharging.
On some chargers, the NIMH mode is for transmitter packs. If you are having probs with your sanyo 3000's, and they are HV's, I would be tempted to try the NiCD mode, as these cells can handle punishment. Whatever you do, make sure you try it first on a charge at home so you can monitor the pack constantly and use the advice above like monitoring the temp and if possible the voltage dropback. Generally, you will then be able to pick up signals before a pack fries....like it getting really really HOT: flaming:
Once you have it sussed at home, then try it at the track.
The best piece of advice here comes from your own last post,
ie: ask where you bought it from. If that fails, ask someone at your local track.