* Flywheel Bolts: The most likely culprit is loose or missing flywheel bolts. These bolts hold the flywheel to the crankshaft. If they're loose or missing, the flywheel can wobble, causing a horrible rattling sound and affecting engine performance. This is a serious issue that needs immediate attention to avoid catastrophic engine damage.
* Transmission Problems: While less likely if the clutch itself was replaced *correctly*, improper installation of the transmission could have damaged the input shaft, bearings, or other internal components. This could manifest as a rattle and poor acceleration.
* Clutch Alignment: Even if the clutch *parts* are new, an improperly aligned clutch disc or pressure plate will cause problems. This could lead to a shudder or rattle, especially under acceleration.
* Driveshaft/U-Joint Issues: While less likely to be directly related to the clutch job, it's possible something was disturbed during the transmission removal process. A worn or damaged U-joint in the driveshaft can cause rattling and poor acceleration.
* Loose or Damaged Parts: During the clutch replacement, other components might have been loosened or damaged. Double-check all bolts and connections related to the transmission and engine.
What to do:
1. Do NOT drive the car further. Continuing to drive with a rattling noise from the drivetrain could cause significant damage.
2. Return to the mechanic who performed the clutch replacement: This is the first and best step. They should diagnose and correct their work. If they refuse to take responsibility, you'll need to get a second opinion.
3. If you're doing it yourself: It's very dangerous to work on this kind of problem without experience. Unless you're very familiar with transmissions and engines, you should *not* attempt any repairs yourself. The risk of further damage is too high.
In short, the rattling and poor acceleration are likely related to the clutch replacement. Get it checked immediately by a qualified mechanic. Ignoring this could lead to extensive and costly engine repairs.