There is a whistle on the throttle of the old Jetta.

The possible reasons are: due to the clearance between the hydraulic valve tappet and the cam (or valve seat). Abnormal noise caused by too high or too low crankcase oil level requires checking the engine oil level. Abnormal sound caused by worn valve guide. Abnormal noise caused by low oil pressure.

Solution: replace the hydraulic tappet; If the abnormal sound is caused by the wear of the valve guide, it is necessary to wrap the valve guide and install the valve with a heavy valve stem. If the engine oil is too thin, it is necessary to replace the engine oil with appropriate viscosity; Abnormal sound caused by low oil pressure needs to be checked.