Nissan Sentra 2009 Problem

Hi All,
I am having a nissan sentra 2009 FE+ model.
When I am starting my engine and then put the gear to drive, then when my car starts moving and gets speed around 5miles/hr then a metal hitting(sound is not sharp) kind of sound is coming from the front down side only once. This is just coming only once and then no issue with the driving. I can drive then without any sound.Then if I keep the car in parking gear but does not turn off the engine, Then if I start again with driving gear, no sound comes.
But if I park my car and completely turn off the engine. Then I start my engine and put the gear in driving and start moving. Then as soon as it gets some speed around 5miles/hr the sound comes again once.
So basically to get the sound ,
1.engine should be in off state.
2.I have to turn on the engine on and start driving.
3.Once I get some speed around 5miles/our, getting the sound of something hitting.
Can you please advise what is this sound about.
Last year I changed my CVT and rear struts . After this change I started getting this sound.initially could not identify in which condition sound is coming.
I am having a nissan sentra 2009 FE+ model.
When I am starting my engine and then put the gear to drive, then when my car starts moving and gets speed around 5miles/hr then a metal hitting(sound is not sharp) kind of sound is coming from the front down side only once. This is just coming only once and then no issue with the driving. I can drive then without any sound.Then if I keep the car in parking gear but does not turn off the engine, Then if I start again with driving gear, no sound comes.
But if I park my car and completely turn off the engine. Then I start my engine and put the gear in driving and start moving. Then as soon as it gets some speed around 5miles/hr the sound comes again once.
So basically to get the sound ,
1.engine should be in off state.
2.I have to turn on the engine on and start driving.
3.Once I get some speed around 5miles/our, getting the sound of something hitting.
Can you please advise what is this sound about.
Last year I changed my CVT and rear struts . After this change I started getting this sound.initially could not identify in which condition sound is coming.
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