>>4434952>dust on sensorWill be in every photo regardless of settings. Not exactly difficult to clean yourself with swabs and a blower, but if you're not confident after watching a youtube video pay a shop to do it.
>dust on rear/front lens elementWill become less apparent at wide apertures (f/2, f/4 etc.) and more visible as you stop down (f/8, f11+). An easy test is to take a photo of a single-coloured wall or piece of paper with the aperture super dooper closed (f/22, f/32). If it becomes more visible as you do this, it's somewhere on/in the lens. Rear element dust is more noticeable than front element dust.
>dust inside lensCan't really clean it out without disassembly. Would not recommend to anyone for any lens that contains electronics, and only to those reasonably confident on a manual lens. Shops may offer to clean it out but many refuse since it's such a fucking difficult job for most lenses for such little reward.
If the camera was just sitting and doing nothing in a closed environment, I can't imagine the lens is clogged with dust inside. It's most likely sensor dust or rear/front element dust.