Engine sounds like a jet engine accelerating then slows when stopping.

What is your question?

My impala started making this sound about 2 wks ago. When I accelerate by pushing the gas down and get to about 25-30mph or higher it sounds like a jet taking off where it gathers speed very quickly. I do not press any differently on the gas than when I used to. When I press on the brake to slow or just take my foot off the gas and don't press on the brake the engine begins to slow and sounds like a jet engine cooling down or coming to a stop. My check engine oil light came on but the oil is about 1/2 full and I know it is not in need of a change but figure we didn't reset the gauge when last changed. Any ideas on what this is and estimate of cost to repair? Thank you!