Weird noise coming from bottom bracket area

[nameused]

Ok, so recently I was out mountain biking and as I was climbing a steep section of the trail, my cranks felt like they skipped a few teeth on the gears or something slipped, as they spun but didn't move the back tire any. I checked the gears on the front and the cranks and everything looked fine. I checked the cranks and they were tightened all the way. However when I've been riding lately on the road, there is this sound that sounds like metal hitting metal and it's coming from the crank/bottom bracket area. It only happens when I'm riding hard and speeding up, once I get going it stops making the noise. Anyone know what this might be? I live in a rather remote area, so I have to order everything and I'd rather find out what the problem is before I order something. Thanks.