If have so, you had been struck bey an earworm. If have so, you had been struck by an earworm.

If have so, you hadve been struck bey an earworm. If have so, you have been struck by an earworm.

If you have so, you hadve been struck bey an earworm. If you have, you have been struck by an earworm.

It is normal for everyone to be plagued by them a few times a week. It is normal for one to be plagued by them a few times a week.

We use the word "one" to make general statements like this.

It is normal (for everyone) to be plagued by them a few times a week. It is normal (for everyone) to be plagued by them a few times a week.

Perhaps better to omit the part in parentheses.

It is normtypical for everyone to be plagued by them a (few times) a week. It is typical for everyone to be plagued by them a (few times) a week.

in (): Optionally you can say a "couple of times"

Scientists have only hypothesesized what causes this phenomenon. Scientists have only hypothesized what causes this phenomenon.

Scientists have onlynothing but hypotheses on what causes this phenomenon. Scientists have nothing but hypotheses on what causes this phenomenon.

Fine to say "only", but better like this in my opinion.

Scientists have onlmany hypotheses about what causes (this phenomenon). Scientists have many hypotheses about what causes (this phenomenon).

(): simply saying earworms is more concise and less wordy.

One of them points out that in some way they resemble habits triggered by music that can't be shaken off. One of them points out that in some way they resemble habits triggered by music that can't be shaken off.

One of them points out that in some way thethey may resemble habits. One points out that they may resemble habits.

Triggered by music can't be shaken off.

Triggered by music which can't be shaken off. Triggered by music which can't be shaken off.

Triggered by music For example, one could be triggered by certain music/tunes and (can't be shaken off). For example, one could be triggered by certain music/tunes and (can't be shaken off).

Not sure what you mean in ()

Another fact worth considering fact is our inability to cut and whistle a certain tune out of the earworm. Another fact worth considering is our inability to cut and whistle a certain tune out of the earworm.

Another fact worth considering fact is our inability to (cut and) whistle a certain tune out of the earworm. Another fact worth considering is our inability to (cut and) whistle a certain tune out of the earworm.

Not sure what cut means here.

Another worth considering fact is oOur inability to cuinterrupt and whistle a certainnother tune out of the earworm. Our inability to interrupt and whistle another tune out of the earworm.

when you say cut, do you mean interrupt?

Once they start churning in our head it is almost impossible to interrupt this process and play in ain the middle. Once they start churning in our head it is almost impossible to interrupt this process in the middle.

Once they start churning in our head it is almost impossible to interrupt this process (and play in a middle). Once they start churning in our head it is almost impossible to interrupt this process (and play in a middle).

Not certain what the last part is supposed to mean.

Once they start churning in our head it is almost impossible to interrupt this process (and play in athe middle). Once they start churning in our head it is almost impossible to interrupt this process (and play in the middle).

not sure what you mean in (), but omitting it still makes a proper sentence

What makes matters worse for people is being surrounded by music almost everywhere. What makes matters worse for people is being surrounded by music almost everywhere.

What makes the matter (or matters) worse for people is being surrounded by music almost everywhere. What makes the matter (or matters) worse for people is being surrounded by music almost everywhere.

It seems to exacerbate our situation. It seems to exacerbate our situation.

A bit short and simple for the ending sentence.