If its a 'twang' type noise - make sure the springs are correctly located in their spring seats. Have the springs accidentally been fitted upside down (especially if you are getting rear-end noise).
And I'd tend to agree with the failing top mounts. The have a bearing in them, and it is fairly common for these to partially seize. Try teasing up the plastic scuttle panel above the top mounts, get a helper to slowly turn the steering wheel from lock to lock, whilst you watch the top mounts for any jerkyness, then hold the top mounts trying to feel for any.