There isn't always extra volume when stocks run up or down, but...

There isn't always extra volume when stocks run up or down, but when there is it is provided by a mass of people wishing to buy or sell. Duster announcements= a lot of people wanting to get out of the stock, which creates the volume, and vice versa of course. If there really were large investment houses buying in, you'd be seeing disclosure of holdings announcements.

Not to mention, what you're describing isn't market manipulation at all, it's just an investment house buying shares at the market rate and then selling them at a market rate. Just because they might be using millions rather than thousands doesn't make it manipulation.

And I'd like to reiterate- the absence of holdings announcements proves that this hasn't happened.