Possible loose strut mount. Have someone look under the hood while you are bouncing the car up and down-look for any movement. Also, try this; raise the car up on the jack, put it on jackstands if you have them, and shake the wheel back and forth and up and down, again looking for movement. If you do this, block the wheels on the ground and be careful not to shake it too much and tip the jack and let the car come down. Can you tell if it's coming from the front or the back? You might want to check each wheel in this manner. looking for movement or loose components. Check stabilizer bar also.