Prius engine noise

[pwuser154960645744]

AoA! I’m facing an issue with my 2014 Prius. When i start the car in morning the engine sound is high and then after a few seconds it becomes normal. Also while driving the engine makes a bit noise when it shifts from battery to engine. What could be the problem?
P.S. The car shifts to battery mode fine when i lift foot from the gas pedal while driving and I’ve tried putting high octane too.

[streetmachines101]

Are you sure that the sound is coming from the engine? Brake booster pump usually makes noise at startup which is completely normal.

[raosahb]

AA, Have you solved the issue or still observing?
Just curious if the sound is gar gar type? if so it may be due to clogged/weak injectors. Just check the injectors flow and get it clean. This will also be evident from spark plugs. At least one of spark plug will be discoloured from others.