You could be describing lots of things. Scraping noise could be an issue with something scraping against the flywheel such as the coil or brake. It may be helpful to tell us what equipment and engine this is and define the noise a bit better if you can.

What kind of metal to metal sound, scraping or knocking?

IF knocking, check the motor mount bolts.

Walt Conner

It's possible the blade is loose or bent, as well as loose motor mounts as Walt said. Worst case, it's getting ready to throw a rod. Have you checked the oil?

"I was cutting the grass last summer and out of the blue the engine starting making this awful metal on metal sound. It gets louder when I apply more gas."

It might be helpful if you posted the make, model and type numbers of the engine. For example, the counter weights of some B&S engines on rare occasion, come apart making noise like this and evenually, a hole in the engine.

Walt Conner

It's an old craftsman mower, 10 hp / 5 speed riding mower.

It runs fine. I mean I get the same sound regardless if the blade is engaged or not. I've already checked the entire blade housing and the sound is coming from within the engine itself....could it be a thrown rod?

When I say the engine runs fine I just mean that it starts and runs around but is so loud that the neighbors come out asking if I'm alright because the noise is so loud.

I found a picture of the lawn mower on line. Sorry it's so small..

Here is a link that might be useful:

Does the noise occur at an idle?
Is the noise rotational - does it increase with engine speed?
With the engine at an idle try running the speed up rapidly. A loose con rod bearing will usually give a much sharper rapping sound under those conditions.

i'm sorry but if the noise is internal to the engine runnign it is ONLY going to make things worse. you need to pull teh engine and see what is going on, not jsut keep running it until it dies. and it likely will die soon. you could possibly still be able to rebuild it at this point, but once it tosses a rod thru the block you may be SOL.

Well wackylawnmowerman you still did not post the make and model number of the engine. It may surprise you to know Craftsman used more than one 10 hp engine. Craftsman 10 hp 5 speed doesn't tell anything.

But that is OK, perhaps others will help, I am out of here.

By the way, a noise loud enough to bring people out of the house to see if you are OK is not a connecting rod, it would have been gone long ago.

Walt Conner

Perhaps something in the starter mechanism is hanging up?
If so, it will manifest itself into a no-start condition
soon.

My B&S Troy-Bilt self propelled mower recently started making a noise like this. If I run it, the tapping gets louder. The blade is not bent or anything. It started when I was mowing a lawn without hitting anything.

Hey walt2002 can I email or chat with u over a Briggs and Stratton opposed twin?

Hey guys, first post so please bare with me. I've got a 2009 John Deere LA125 with a 21 HP single valve Briggs. 108 hours clocked and my @sshole neighbor left some of his old barbed-wire out on the property line. I hit it, the mower didn't die, I put it in reverse and went along my business. 4 days later I started it up and at idle it made a metal on metal scraping noise. I thought maybe I had some of the fencing in the deck. Checked and all was fine. Blades are in good shape, I think...problem is I noticed at mowing speed I hear no sound. When I disengage and the mower sits at idle with the blade moving at an idle speed the noise comes...It happens at every deck setting...I've even spray painted the interior of the deck to see if there's a place the blades may be hitting. What am I missing? Thanks

Wire tight to the hub?