What kind of GPU do you have?
Does it have multiple fans on it?

If they have a sticker on the middle part (circled with red) that's somewhat bulged it could mean the bearing on the fan is busted and requires at least a replacement fan.
More likely the middle is going to be covered somehow (unless it's an older GPU) and diagnosing exact cause is going to be harder, but the description makes it sound like a fan bearing failure due to wear and tear, causing overheating of the GPU under heavy workload.