* Transmission issues: This is a strong possibility. A slipping clutch (if manual), a worn transmission, or a problem with the final drive gears could prevent the engine from efficiently transferring power to the wheels at higher speeds. The rumbling sound points towards a mechanical problem within the transmission.
* Engine problems: While less likely given the description, a restriction in the exhaust system (e.g., a clogged catalytic converter) or insufficient air intake (dirty air filter, blocked intake) could limit power at higher RPMs. However, these usually manifest as a loss of power across the rev range rather than just at a specific speed.
* Fuel delivery issues: A clogged fuel filter or a failing fuel pump could starve the engine of fuel, preventing it from reaching its full potential at higher speeds. This is less likely to cause the rumble though.
* Drive shaft or axle issues: A worn CV joint or a problem with the drive shaft could lead to vibrations and a loss of power, especially at higher speeds. The rumbling could indicate this.
What to do:
1. Check the obvious: Start by checking the basics: tire pressure, air filter, and ensure there are no obvious visual problems with the exhaust system or undercarriage.
2. Listen carefully to the rumble: Try to pinpoint where the rumble is coming from. Is it coming from the engine bay, the transmission area, or the rear of the car? This helps diagnose the problem's location.
3. Professional Inspection: This is crucial. Take your car to a qualified mechanic. Describing the symptoms (60mph limit, loud rumble at higher speeds in top gear) will help them diagnose the problem accurately. They have the tools and expertise to diagnose transmission problems, engine issues, or drive train failures. Guessing can be costly. A proper diagnosis is essential before you undertake any repairs.
Don't continue driving the car extensively with this problem, as you risk causing further damage to the transmission or other components.
