good day!

I just want to consult if may problem yung transmission ng car namin. Ride is 2003 diesel adventure SS, manual, 90k mileage. Ok naman yung shifting on gears 1 to 3, even 4th gear. Problem is when coasting using 4th gear. If im engaged in 4th, tapos i gradually applied the brakes to slow down, I hear rattling sounds sa ilalim, parang nanggagaling sa may propeller. It only occurs kapag i slowed down to about 15kph and not stepping on the gas. I can even feel the vibration on the stick shift. But if i step on the gas and the engine revs to pick up speed, the sound disappears . I had a change oil done about 2 months ago, and the gear oil was checked and refilled at the gas station.

Walang problem with regards to shifting or pulling power. 5th gear and reverse has no problems too. Dun lang talaga sa 4th gear coasting at low speed.

I'm just curious if this is a normal occurrence sa adventure for its age, or may problem na yung transmission nya?

Insights are highly appreciated. TIA.