nick49

Exiting my neighborhood there is a gutter that I need to slow a bit for then a right turn and an immediate down grade for about 500 feet. Then another 90 degree right hander.

Both of these right hand turns, 10-20 MPH cause a knocking sound almost like a pendulum swinging a weight. There are 3-4 successive knocks and they only come from the right rear behind the rear seat area.

One time I though it was a rear suspension component but all that has been replaced with coilovers, dogbones and sway bar. I checked everything else suspension wise and it's OK.

It doesn't happen when turning sharply right on a totally smooth road or in the canyon twisties. Never happens when turning left under any circumstances. It seems to happen only when the suspension may have been loaded momentarily and possibly unloaded too.

I'm thinking possibly a seat belt device or roll bar activation component?

Any ideas?

LexVan

Motor mount(s).

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nick49

Thanks for the quick reply. Is that a guess, a most likely, or with a degree of certainty?

My car has 27K miles, started with less than 20K. Never tracked, always garaged, not driven in inclement weather, previously a Las Vegas car. Not doubting you, just thinking they should last a bit longer under those conditions.

LexVan

It was my WAG.

Top up? Top down? Same?

Buckle the rear seat belts. Any better?

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nick49

Top up for sure, I'll try top down and buckling all seat belts around a pillow.

Thanks again, I'll post results when tried.

LexVan

Blip your throttle and have someone stand behind (or video with your phone) and observe if the exhaust tips dip excessively. If they do. I'd WAG again motor mounts.

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Dock

So there is no knocking during any other right hand turns?

Are both of the right hand turns you describe downhill?

nick49

The first turn is a slight down grade, the second more so. The common factor in both is the gutter before the first turn and slightly bumpy pavement before and in the second. The suspension is loaded and unloaded while in both turns. I'm thinking that's why it never does it on smooth roads even if driven aggressively. I have noticed it happen a few times in other areas too and it always happens with rough pavement while taking a turn.

Also I have had my top half way up in the service position and took a look under and around looking for something amiss and could nothing.

nick49

Drove my car first time since my original post, top down, no passengers with all seat belts fastened. I drove the route that triggers the knocks and all was quiet. I also noticed the car much quieter than normal over rough road sections and bumps all the way into work today.

For now, I'm convinced the majority of the knocking sound has to do with seat belts in the retracted mode. I believe there is a pendulum mechanism that senses cornering inertia and locks the belt tight. I have felt this when driving somewhat aggressive. If I lean more I shall post my findings.

Thanks Lex for the buckling belt idea.